There are a couple of ways to test if it's working as well, if you're logged in as an admin.
If you're using ImageMagick, then you'd use
ubbthreads.php?ubb=captcha&test=1&type=im
If you're using GD2, then you'd use
ubbthreads.php?ubb=captcha&test=1&type=gd
OK, Mogrify? Ok, so I'm old
That is a new word. I saw the GD2 in the drop down. That was the only choice beside disable so I clicked that.
Where do I put this? ubbthreads.php?ubb=captcha&test=1&type=gd
Wow do I feel old and helpless